Oscar the Grouch is reading This Little Worm to Slimey, when Telly, Rosita and Lexine interrupt their story time looking for Big Bird. Oscar says he's at the Park, which is where the group is headed to for their fun activities. Slimey wants to go there with the group, but Oscar denies him going anywhere with big kids, until they convince Oscar it's fine with them. Lexine gives Slimey a ride as they head to the park, while Oscar bids them to be careful. ("Before you know it, they're leavin' the nest...")

At the park, Lexine asks who wants to ride the see-saw with Slimey, but everyone can't decide who goes first. Lexine suggests cooperating, but it also backfires, so she picks Big Bird to go first, then Telly, then Rosita, then herself. Big Bird sits on the see-saw, but his heavy size causes Slimey to fly away. The group worries where he could be as they thoroughly search the park.

SCENE 3

The group hasn't found Slimey anywhere, so Big Bird decides to ask somebody for help, namely the "lady with a worm on her hat" nearby. Initially unaware, she learns the worm is with them, and has Lexine take Slimey off her bonnet. After she leaves, everyone begins their next activity – hide-and-seek. Slimey gets extra time to hide first since he's slow, but after the others return to home free, he becomes lost again.

SCENE 4

Slimey is still nowhere to be seen, until Telly spots him crawling on Big Bird's feather, and the group rejoices that Slimey's back. Big Bird reveals he has an obligation with Snuffy and must head out, while the group now goes to buy balloons. The vendor (played by Brian Muehl) hands them three balloons, but Telly points out he's missed one, so the vendor gives a fourth one for Slimey. While everyone debates over who has money to pay, Slimey suddenly starts rising up with the balloon, putting the group in a real pickle!

SCENE 5

Oscar berates the group for letting Slimey into the sky and not being careful enough. In desperation, everyone tries calling for Slimey, when out of the blue, he arrives back on Sesame Street with a parachute. It turns out Oscar's packed one in his backpack in case, and in a parental manner, he reminds Slimey to not get lost again. However, Oscar gets caught in trying to say that he loves him, getting teased by the others for his Grouchy support. Big Bird announces the sponsors.